/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.scripting.bsh;

import java.io.IOException;

import bsh.EvalError;

import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.lang.Nullable;
import org.springframework.scripting.ScriptCompilationException;
import org.springframework.scripting.ScriptFactory;
import org.springframework.scripting.ScriptSource;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;

/**
 * {@link org.springframework.scripting.ScriptFactory} implementation
 * for a BeanShell script.
 *
 * <p>Typically used in combination with a
 * {@link org.springframework.scripting.support.ScriptFactoryPostProcessor};
 * see the latter's javadoc for a configuration example.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @see BshScriptUtils
 * @see org.springframework.scripting.support.ScriptFactoryPostProcessor
 * @since 2.0
 */
public class BshScriptFactory implements ScriptFactory, BeanClassLoaderAware {

    private final String scriptSourceLocator;

    @Nullable
    private final Class<?>[] scriptInterfaces;
    private final Object scriptClassMonitor = new Object();
    @Nullable
    private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();
    @Nullable
    private Class<?> scriptClass;
    private boolean wasModifiedForTypeCheck = false;


    /**
     * Create a new BshScriptFactory for the given script source.
     * <p>With this {@code BshScriptFactory} variant, the script needs to
     * declare a full class or return an actual instance of the scripted object.
     *
     * @param scriptSourceLocator a locator that points to the source of the script.
     * Interpreted by the post-processor that actually creates the script.
     */
    public BshScriptFactory(String scriptSourceLocator) {
        Assert.hasText(scriptSourceLocator, "'scriptSourceLocator' must not be empty");
        this.scriptSourceLocator = scriptSourceLocator;
        this.scriptInterfaces = null;
    }

    /**
     * Create a new BshScriptFactory for the given script source.
     * <p>The script may either be a simple script that needs a corresponding proxy
     * generated (implementing the specified interfaces), or declare a full class
     * or return an actual instance of the scripted object (in which case the
     * specified interfaces, if any, need to be implemented by that class/instance).
     *
     * @param scriptSourceLocator a locator that points to the source of the script.
     * Interpreted by the post-processor that actually creates the script.
     * @param scriptInterfaces the Java interfaces that the scripted object
     * is supposed to implement (may be {@code null})
     */
    public BshScriptFactory(String scriptSourceLocator, @Nullable Class<?>... scriptInterfaces) {
        Assert.hasText(scriptSourceLocator, "'scriptSourceLocator' must not be empty");
        this.scriptSourceLocator = scriptSourceLocator;
        this.scriptInterfaces = scriptInterfaces;
    }


    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        this.beanClassLoader = classLoader;
    }


    @Override
    public String getScriptSourceLocator() {
        return this.scriptSourceLocator;
    }

    @Override
    @Nullable
    public Class<?>[] getScriptInterfaces() {
        return this.scriptInterfaces;
    }

    /**
     * BeanShell scripts do require a config interface.
     */
    @Override
    public boolean requiresConfigInterface() {
        return true;
    }

    /**
     * Load and parse the BeanShell script via {@link BshScriptUtils}.
     *
     * @see BshScriptUtils#createBshObject(String, Class[], ClassLoader)
     */
    @Override
    @Nullable
    public Object getScriptedObject(ScriptSource scriptSource, @Nullable Class<?>... actualInterfaces)
            throws IOException, ScriptCompilationException {

        Class<?> clazz;

        try {
            synchronized (this.scriptClassMonitor) {
                boolean requiresScriptEvaluation = (this.wasModifiedForTypeCheck && this.scriptClass == null);
                this.wasModifiedForTypeCheck = false;

                if (scriptSource.isModified() || requiresScriptEvaluation) {
                    // New script content: Let's check whether it evaluates to a Class.
                    Object result = BshScriptUtils.evaluateBshScript(
                            scriptSource.getScriptAsString(), actualInterfaces, this.beanClassLoader);
                    if (result instanceof Class) {
                        // A Class: We'll cache the Class here and create an instance
                        // outside of the synchronized block.
                        this.scriptClass = (Class<?>) result;
                    } else {
                        // Not a Class: OK, we'll simply create BeanShell objects
                        // through evaluating the script for every call later on.
                        // For this first-time check, let's simply return the
                        // already evaluated object.
                        return result;
                    }
                }
                clazz = this.scriptClass;
            }
        } catch (EvalError ex) {
            this.scriptClass = null;
            throw new ScriptCompilationException(scriptSource, ex);
        }

        if (clazz != null) {
            // A Class: We need to create an instance for every call.
            try {
                return ReflectionUtils.accessibleConstructor(clazz).newInstance();
            } catch (Throwable ex) {
                throw new ScriptCompilationException(
                        scriptSource, "Could not instantiate script class: " + clazz.getName(), ex);
            }
        } else {
            // Not a Class: We need to evaluate the script for every call.
            try {
                return BshScriptUtils.createBshObject(
                        scriptSource.getScriptAsString(), actualInterfaces, this.beanClassLoader);
            } catch (EvalError ex) {
                throw new ScriptCompilationException(scriptSource, ex);
            }
        }
    }

    @Override
    @Nullable
    public Class<?> getScriptedObjectType(ScriptSource scriptSource)
            throws IOException, ScriptCompilationException {

        synchronized (this.scriptClassMonitor) {
            try {
                if (scriptSource.isModified()) {
                    // New script content: Let's check whether it evaluates to a Class.
                    this.wasModifiedForTypeCheck = true;
                    this.scriptClass = BshScriptUtils.determineBshObjectType(
                            scriptSource.getScriptAsString(), this.beanClassLoader);
                }
                return this.scriptClass;
            } catch (EvalError ex) {
                this.scriptClass = null;
                throw new ScriptCompilationException(scriptSource, ex);
            }
        }
    }

    @Override
    public boolean requiresScriptedObjectRefresh(ScriptSource scriptSource) {
        synchronized (this.scriptClassMonitor) {
            return (scriptSource.isModified() || this.wasModifiedForTypeCheck);
        }
    }


    @Override
    public String toString() {
        return "BshScriptFactory: script source locator [" + this.scriptSourceLocator + "]";
    }

}
